A childhood belief about skin

I have this birthmark on my arm that looks like a brown blotch, not a puffy freaky hairy thing, that with a little imagination looks like the jet engine on the wing of an airplane when viewed at lets say a 3/4 angle. When I was real young, maybe 4-5 years old, I used to think it was a design or blueprint for some weird gizmo of sorts that I never knew the purpose for. I hid it from people back then, not because of that though it might've been the secondary reason, I still prefer not to show it to this very day (you wouldn't believe how many people dunno what a birthmark is nowadays and ask or give weird looks).